Devulcanization is a method of recycling waste thermoset elastomeric material to produce a material that can be revulcanized into useful products. A thermoset elastomer results from a polymer that is irreversibly cured. Prior art processes for devulcanization use chemical, ultrasonic, biological with microorganisms, mechanical, microwave or steam techniques.
One such mechanical process known as high shear mixing (HSM) provides extremely high levels of shear and extensional stress, thereby inducing chemical reactions in the material being processed. U.S. Pat. No. 7,461,970, assigned to the applicant, describes such a process. It uses a mixing apparatus having two opposing mixing members rotatable relative to one another about an axis and that have facing surfaces which extend away from the axis to define a mixing chamber. An array of mixing formations on at least one of the surfaces acts to mix material and propel the material within the chamber toward the axis. This mechanical process has demonstrated the ability to un-crosslink thermoset elastomers using shear energy such that approximately 60% of the original physical properties of the materials are recovered.
Other mechanical processes include the step of adding chemicals to the material in the mixing chamber. However, these chemicals are extremely toxic and cause toxic gases to be emitted during the process. Today these processes are only used in countries where there are no controls on toxic emissions or enforceable regulations to protect the environment from such contamination.
WO 03/014206A1, assigned to the applicant describes a process for treatment of cross-linked elastomers such that a predetermined portion of the untreated material remains as vulcanized granules to thereby produce a flowable material comprising vulcanised elastomer dispersed in a matrix of devulcanized elastomer.